Process for separating normal aliphatic hydrocarbons from organic mixtures thereof



Patented Mar. 18, 1952 PROCESS FOR SEPARAT ING' NORMAL A'LI- PHATIC HYDROCARBON S FROM GRGANIC MIXTURES THEREOF Howard V. Hess, Beacon, George 13. Arnold, Glenhaln, and James K. Truitt, Beacon, N. Y., assignors to The Texas Company, New York, N. Y., a corporation of Delaware No Drawing. Application November 16, 1949, Serial No. 127,788

Claims. 1

This invention relates to a process for separating normal aliphatic hydrocarbons from naphthenes, isoaliphatic, heterocyclic and aromatic hydrocarbons. More specifically, this invention provides a process whereby normal aliphatic hydrocarbons are isolated from hydrocarbon mixtures.

In accordance with the process of this invention, normal aliphatic hydrocarbons are separated from a mixture containing them in combination with isoaliphatic, naphthenic, heterocyclic and aromatic hydrocarbons by contacting the mixture with 4,4-dinitrodiphenyl whereby there is formed a solid complex consisting of 4,4- dinitrodiphenyl and normal aliphatic hydrocarbons. The complex so formed is readily separated, since it is ordinarily insoluble in the mixture at atmospheric conditions. We have discovered that 4,4-dinitrodiphenyl is a selective complexing agent for normal aliphatics containing more than six carbon atoms. Alpha-substituted normal aliphatics, such as n-octyl alcohol, noctyl benzene and n-decylchloride and alpha substituted normal aliphatic olefins such as lbromo-octene-l form solid complexes with 4,4- dinitrodiphenyl.

The process of the invention is extremely useful in petroleum refining. Petroleum fractions, such as, lubricating oils can be freed from undesirable constituents, such as substantialy straight chain waxes by contacting with 4,4-dinitrodiphenyl in accordance with the process of this invention. Refrigerator oils of superior grade are produced by dewaxing oil with 4,4-dinitrodiphenyl; gas oil can be dewaxed by the procedure of this invention to give a diesel oil of very low pour which is very useful in cold weather operation. The process may be used as a substitute or as a supplement to conventional solvent dewaxing procedures, such as methylethylketone-benzol dewaxing which involve the use of solvents at sub-atmospheric temperatures. The main application of the process of this invention is in the dewaxing of gas oils and as a supplement to conventional solvent dewaxing procedures in the formation of specialty oils.

It is apparent that the applicants discovery that 4,4'-dim'trodiphenyl form solid complexes with normal aliphatic hydrocarbons is useful,

either as a means of isolating and recovering normal aliphatic hydrocarbons from mixtures or as a means of freeing mixtures of normal hydrocarbons where their presence is undesirable. The dewaxing of gas oils and lubricating oil fractions is an exemplification of the usefulness of the invention to accomplish the latter objective, whereas the isolation of normal alpha-olefins from the gas oil fraction of synthetic fuel exemplifies the usefulness of the invention for the former objective. As has been indicated previously, the main commercial usefulness of the process of this invention resides in the freeing of gas oil and lubricating oil fractions of undesirable constituents.

4,4.'-dinitrodiphenyl forms crystalline complexes with straight chain hydrocarbons containing more than six carbon atoms. The straight chain hydrocarbons can be alkanes, 'alkenes, alkadienes or alkynes. Normal aliphatic hydrocarbons containing ten or more carbon atoms form crystalline complexes more rapidly at a higher temperature than do lower molecular weight normal hydrocarbons, such as, hexane and heptene. Normal hydrocarbons containing ten or more carbon atoms form crystalline complexes when contacted with 4,4'-dinitrodipheny1 at atmospheric temperatures and. at temperatures up to about 150 F. However, normal hydrocarbons containing less than ten carbon atoms and more than six carbon atoms require colder tom:

peratures of the order of 40 F. to 20 F. before there are formed solid complexes thereof with 4,4. -dinitrodiphenyl.

Alpha-substituted normal aliphatic hydrocarbons behave similarly to the normal aliphatic hydrocarbons in complexing with 4,4'-dinitrodiphenyl. The alpha-substituted normal hydrocarbons containing eight or more carbon atoms, such as, normal decylchloride, normal decyl alcohol,

etc. form solid complexes at atmospheric conditions, whereas normal hydrocarbons containing less than eight carbon atoms, such as, n-hexanol and l-bromoheptene-2 and hexene only form the solid complexes at temperatures in the range of 40 to 20 F.

4,4'-dinitrodiphenyl has a structural formula as follows: 1

This compound despite the presence of two nitro groups is very stable to heat.

Complex formation is ordinarily effected at atmospheric conditions. This characteristic of complex formation is one of the major advan-' tages of the uses of the process of this invention in dewaxing lubricating oil fractions. Temperatures of to F. areordinarily employed for complexing 4,4'-dinitrodiphenyl with normal aliphatic hydrocarbons containing more than 3 nine carbon atoms. The temperature should be maintained below 160 F. during contact of the organic mixtures with the complexing agent in order to efiect'formation of the solid complex.

Atmospheric pressure is ordinarily employed for forming crystalline complexes of this invention. pressures may also be employed, as there appears to be no criticalness with respect to pressure in the formation of complexes of 4,4'dinitrodiphenyl and normal hydrocarbons.

Formation of crystalline complexes between 4,4-dinitrodiphenyl and normal hydrocarbons can be effected by a variety of procedures. One procedure involves contacting a solution containing normal hydrocarbons with a bed of 4,4dinitrodiphenyl whereby crystalline complex forms in the bed of complexing agent and the eiiluent from the bed is substantially free of normal aliphatic hydrocarbons. It is possible to employ a surface-active supporting material, such as, Filter Cel, silica gel, diatomaceous earth, bauxite, etc. in the bed of complexing agent in order to efiect additional refining action and facilitate passage of oil therethrough. A surface-inactive material such as ceramic packing may also be mixed with the 4,4-dinitrodiphenyl to facilitate passage of the oil therethrough, This procedure is advantageously employed when the objective of complex formation is to free an oil fraction of normal aliphatic constituents, for example, in

preparation of refrigerator oil by dewaxing a lubricating oil of low wax content.

When the mixture containing normal hydrocarbons is contacted with a bed of complexing agent, which is advantageously supported on a surface-active material or surface-inactive mate rial, it is desirable to wet the bed of complexing agent with a polar compound; aliphatic alcohols such as methanol or ethanol, aliphatic nitriles such as acetonitrile, ketones such as acetone or water are examples of polar compounds that may be employed. Formation of complex in direct contact of a hydrocarbon mixture with complexing agent is substantially expedited by the presence of a small amount of polar compound.

Another modification of liquid-solid contacting of complex agent and hydrocarbon mixture involves slurrying particles of complexing agent in the mixture with thorough agitation. The presence of small quantities of polar solvent, sufiicient Sub-atmospheric and super-atmospheric to wet the surface of the complexing agent 2.1-

though the amount is not critical, is also recommended in this method of operation. This technique is preferred in small scale operations and I in processes wherein the objective is recovery 'of normal hydrocarbons from the complex.

Another procedure for effecting complex formation involves mixing a saturated or supersaturated solution of complexing agent with the hydrocarbon mixture to be treated. Thorough agitation is also recommended in employing this procedure for complex formation. Solvents which may be used include ketones, such as acetone and methylethyl ketone, nitriles, such as acetonitrile and low molecular weight alcohols, such as ethyl alcohol. It is advisable to select a solvent which has a high solvent capacity for the complexing agent at temperatures up to 125 F. in order to avoid the use of large quantities of solvent. This technique can be used either insmall scale or large scale operation but it is more adapted to the former. Moreover, it is equally eilective whether the objective of the process is to free a hydrocarbon solution of undesirable normal hydrocarbons, such as in dewaxing, or in the isola tion and recovery of normal aliphatic hydrocarbons for a specific use.

The crystalline complex 4,4-dinitrodiphenyl and normal hydrocarbons on alpha-substituted normal hydrocarbons is ordinarily separated from the mixture of isoaliphatic, naphthenic, heterocyclic and aromatic compounds by filtration. However, a simple decantation procedure and centrifugal separators are also employed to remove the crystalline complex from the mixture of hydrocarbons. Separation of the complex from the treated mixtfire is readily eifected using any of various types of filters, such as, rotary filters, filter presses, etc. Centrifugal separation and illtration are the most efiicient and best methods for separating the complex.

After the complex has been separated, it is advisable to wash the complex in order to elute absorbed compounds therefrom. Hydrocarbon solvents, such as, benzene, naphtha fractions and pentane can be employed at atmospheric temperature to free the complex of physically absorbed hydrocarbons. If lower molecular weight hydrocarbons are complexed, washing of the complex is efieeted at reduced temperature with solvents such as isobutane. The use of rotary'filter is particularly advantageous when a washing procedure is employed, since filtration and washing can be effected in a continuous operation.

The normal aliphatics are recovered from the complex by heating to a temperature of about 175 F. at which temperature the crystalline complex decomposes into two phases, consisting of normal hydrocarbons and a solid phase of 4,4- dinitrodiphenyl, which are readily separated by hot filtration. The direct heat breaking of the complex can be modified by the use of solvents for one or other of the constituents of the complex. Thus, the complex may be heated with a solvent, such as, benzene and toluene or naphtha to a temperature above 175 F., whereby the complex is decomposed and there are formed two phases, a liquid phase comprising solvent and dissolved normal hydrocarbons and a solid phase consisting of 4,4-dinitrodiphenyl. Alternatively, the complex may be heated to a temperature of about 150 to 250 F. with a solvent for dinitrodiphenyl having relatively low oil solubility, such as, acetone, methylethylketone and ,acetonitrile whereby the complex is decomposed and there results a two phase liquid system, one layer comprising solvent and dissolved complexing agent and the other comprising normal aliphatic hydrocarbons freed from the crystalline complex. It may be necessary to use superatmospheric pressures when employing low boiling solvents such as acetone for decomposing the complex.

The selection of the procedure to be employed for decomposing the complex into its constituents depends upon the nature of the compounds that are complexed. For example, if a complex comprises 4,4-dinitrodiphef1yl and a normal hydrocarbon of high molecular weight, such as, n-eicosane, poor separation would be effected be tween the complexing agent and the n-paraffin on simple heating, since a substantial quantity of normal hydrocarbons would be physically adlution of the complex into its components.

The objective of the complexing process also materially influences the choice of procedure employed for complex breaking. 'If "the process of the invention is employed to dewax gas oil or lubricating oil, ordinarily the only interest in the complex lies in the recovery'of dinitrodiphenyl for recycle purposes. Accordingly, the procedure employed for breaking the complex is not too important as long as the complexing agent is recovered therefrom. However, when the objective of the complexing process is to isolate normal aliphatic hydrocarbons for further use, then the procedure for recovering the normal hydrocarbons in the complex is selected with a view to recovering the normal aliphatic constituents in the purest form. In such instances, it is advisable to decompose the complex by heating it to a temperature above 175 F. in the presence of a solvent for the complexing agent, such as, methylethylketone; the normal aliphatic hydrocarbon obtained on decomposing the complex can be readily freed of ketone.

The main application of the process of this invention is in dewaxing gas oil and lubricating oil" fractions. Waxy constituents having a normal aliphatic structure are simply separated from gas oil and lubricating oil fractions by contacting the fraction with 4,4-dinitrodiphenyl in accordance with one of the above outlined procedures. It is a simple matter to filter the crystalline complex of n-aliphatic waxy constituents and 4,4'-dinitrodiphenyl from the hydrocarbon fraction. The residual oil is characterized by enhanced lubricating properties and lower pour and haze tests. The application of the process of this invention to dewaxing lubricating oil fractions is illustrated by the following examples:

Example I There was subjected to the process of this invention a turbine oil characterized by the following tests:

Gravity, API 23.6 Viscosity, SSU at 100 F 303 Viscosity, SSU at 130 F 133 Pour point 25 F. Freon haze above 20 F.

9 cc. of this oil was treated at room temperature with 10 g. of 4,4-dinitrodiphenyl and 10 cc. of acetone. After stirring for one hour, the solid complex and excess 4,4'-dinitrodiphenyl was removed by filtration. The filtrate was water washed to remove acetone and dried; 94 cc. of oil was recovered. The treated oil had an indicated Freon haze of -65 F. and a pour point of 25 F.

Example II There was subjected to the process of this invention a wax distillate having a solid point of 70 F. and further characterized by the following properties:

Gravity, API "-32.7 Viscosity, SSU at 210 F 42.6

100 cc. of this wax distillate was stirred for one hour at 175 F. with 50 cc. of acetone and 150 g. of 4,4'-dinitrodiphenyl. The crystalline complex thereby formed was filtered from the wax distillate. The filtrate was stripped to 350 F. to remove acetone and was thereafter tested. The treated oil had a. solid point of +12 F. as contrasted with a solid point of +70 F. for the wax distillate. The yield of dewaxed oil was 77 volume per cent.

5 Example '1'11" 1 There was subjected to the process, of this in, vention a gas oil characterized by the following tests:

This oil was treated with 173 lb./bbl. of 4,4- dinitrodiphenyl and 4.5 gaL/bbl. of acetone for thirty minutes at 75 F. The solid complex of the 4,4-dinitrodiphenyl and normal paraffin hy drocarbons was removed by filtration. The filtrate which amounted to 88.7 weight per cent of the original had a pour point of +5 F. and a solid point of 0 F.

These examples illustrate the dewaxing proper ties of 4,4-dinitrodiphenyl. The oil obtained as a result of the dewaxing procedure detailed in Example 1 is anexcellent refrigerator oil being characterized by extremely low pour and Freon haze tests. It was established by X-ray analysis that the hydrocarbons recovered from the complex separated from turbine oil were normal aliphatic waxes. The oil obtained as a result of the dewaxing process in Example II is substantially free of normal aliphatic waxes, but still contains a substantial portion of aliphatic waxy constituents. The wax recovered from the complex formed in Example II has a high melting point and is useful in the preparation of waterproof coatings. The gas oil obtained in Example III is well suited to cold weather operation of diesel engines and jet engines.

While the process of the invention has been specifically exemplified in the dewaxing of a wax distillate, a turbine oil and gas oils, the process may be used to remove normal hydrocarbons from other types of hydrocarbon fractions. Gasolines may be treated to remove the low octane components thereby upgrading the gasoline.

With viscous feed oils, such as, wax distillate and residual cylinder stocks, diluents may be used to facilitate contact between feed oil and the complexing agent; naphtha hydrocarbons, aromatic hydrocarbons and mixtures thereof can be employed as diluents.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may 'be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A process for isolating a compound select- 7 normal aliphatic compounds'containing 6 to 9 carbon atoms are contacted with 4,4'-dinitrodiphenyl at a temperature of 20 to 40 F.

3. A process according to claim 1 in which normal aliphatic hydrocarbons containing 10 or more carbon atoms are contacted with 4,4dinitrodiphenyl at temperatures of '70 to 120 F.

4. A process according to claim 1 in which the complex is decomposed by heating to a temperature above 175 F.

5. A process for separating normal aliphatic compounds and alpha-susbtituted normal aliphatic compounds containing at least six carbon atoms from an organic mixture thereof which comprises contacting said mixture with 4,4'-dinitrodiphenyl at a temperature less than 160 F. whereby there is formed a solid complex consisting of 4,4-dinitrodiphenyl and normal aliphatic compounds'and separating said complex from said mixture.

6. A process for separating normal aliphatic hydrocarbons from a mixture of hydrocarbons containing at least six carbon atoms which comprese contacting said mixture with 4,4'-dinitrodiphenyl at a temperature less than 160 F. where-- by there is formed a solid complex consisting of n-aliphatic hydrocarbons and 4,4'-dinitrod1- phenyl and separating said complex from said mixture.

'7. A process according to claim 6 in which normal aliphatic hydrocarbons containing 6 to 9 carbon atoms are contacted with 4,4-dimtrodiphenyl at a temperature between -20 and 40 F.

8. A process according to claim 6 in which normal aliphatic hydrocarbons containing 10 or more carbon atoms are contacted with 4,4- dinitrodiphenyl at a temperature between '70 and F.

9. A process according to claim 6 in which the hydrocarbon mixture is a gas oil fraction.

10. A process according to claim 6 in which the hydrocarbon mixture is a lubricating oil fraction.

HOWARD V. HESS. GEORGE B. ARNOLD. JAMES K. TRUITT.

No references cited 

1. A PROCESS FOR ISOLATING A COMPOUND SELECTED FROM THE GROUP CONSISTING OF NORMAL ALIPHATIC HYDROCARBONS AND ALPHA-SUBSTITUTED NORMAL ALIPHATIC HYDROCARBONS CONTAINING AT LEAST SIX CARBON ATOMS FROM MIXTURES OF ORGANIC COMPOUNDS, WHICH COMPRISES CONTACTING SAID MIXTURE WITH 4,4''-DINITRODIPHENYL AT A TEMPERATURE LESS THAN 160* F., WHEREBY A SOLID COMPLEX CONSISTING OF 4,4''-DINITRODIPHENYL AND SAID COMPOUND IS FORMED, SEPARATING SAID COMPLEX FROM SAID MIXTURE AND RECOVERING SAID COMPOUND FROM SAID COMPLEX. 